Gas tank fuel systems providing reduced gasoline vapor loss are becoming increasingly important in the automobile industry to reduce needless loss of fuel. The typical solution to this problem has been to reduce the diameter of at least a section of the fuel tank filler neck. Though this approach has been somewhat successful, it is limited because as the diameter of the filler neck is decreased, the resistance to flow of the gasoline is increased. The increased resistance causes the fill neck to release any pressure buildup, thereby causing the fuel nozzle to shut off before the fuel tank is full. Another design issue is the permeability of the materials from which the fuel tank system is made. Fuel vapors may diffuse through fuel tank system components fabricated from various types of mild steels. Further, such fuel vapor diffusion increases as the mild steel components corrode over time.
Another disadvantage of current filler neck design is the method by which the inlet of the filler neck is flared in order to provide a sufficient diameter to accept the gas nozzle during refueling. Typically, current filler necks are made by a process of repeated reductions and expansions of a seamed welded tube. Thus, through this mechanical process, there is an increasing tendency for the weld to leak as the tube is structurally weakened and thinner diameter tubes are used. Further, many filler necks require a retainer to be fitted to the inlet end in order to provide a sealing surface and an engageable thread for a gas cap.